Functional properties of efferent zones of the motor cortex which project to ipsilateral and contralateral face muscles

In both intact (4 animals) and lesioned (2 preparations with contralateral motor cortex ablation and 1 animal with transection of the rostral two thirds of the corpus callosum) cats, three different types of efferent zones were identified in the face motor cortex by the technique of microstimulation: contralateral, ipsilateral and bilateral efferent zones. The three types of efferent zones had different organizational features such as location, thresholds of effective sites and latencies of motor responses. Mean thresholds of effective sites from ipsilateral and bilateral efferent zones in lesioned animals were not significantly higher than those in intact preparations. In both intact and lesioned animals, neurons endowed with contralateral, bilateral and ipsilateral receptive fields were isolated from the three types of efferent zones.     

Binocular interaction in the parastriatal rat cortex during a change in intensity of one monocular stimulus

Binocular interaction in symmetrical centers of the parastriatal cortex in rats was investigated by the evoked potentials method before and after callosotomy. A model was used in which one eye was always stimulated by flashes of average intensity and the other by flashes of average intensity. The presence of contralateral and ipsilateral facilitation, increasing with the strength of the stimulus, was demonstrated; contralateral facilitation was more effective than ipsilateral. Synergism in the development of the contralateral and ipsilateral effects is emphasized, distinguishing them from the corresponding processes in the striatal cortex. After callosotomy the contralateral and ipsilateral facilitatory effects are intensified.Biological Institute, Leningrad University. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 128–132, March–April, 1973.     

Binocular interaction in the striatal cortex of rats during changes in intensity of a monocular stimulus

Binocular interaction was investigated by the evoked potentials method in symmetrical centers of the rat striatal cortex before and after division of the corpus callosum. One eye was always stimulated by flashes of average intensity and the other by flashes of varied intensity. Contralateral facilitation was shown to be increased with an increase in the strength of stimulation. Ipsilateral facilitation was found to exist and to change into ipsilateral depression. In all cases contralateral effects were stronger than ipsilateral. The reciprocity of contralateral and ipsilateral influences in the striatal cortex is emphasized. Division of the corpus callosum leads to strengthening of the contralateral and ipsilateral facilitatory and depressive influences. Depressive ipsilateral influences are found after callosotomy in response to weaker stimuli than before the operation.Biological Institute, Leningrad University. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 122–127, March–April, 1973.     

Influence of the sensorimotor cortex on single neurons of the nucleus gracilis in the cat

The aim of this study was to investigate the functional role of the cortical projections to gracile nucleus. In unanesthetized cats single nuclear units projecting to the thalamus were tested for microstimulation of cortical foci (area 4) able to evoke single joint movements in contralateral hindlimb. A very significant percentage of gracile cells was influenced, very often in excitatory manner, if their receptive field was overlaying or very close to the joint controlled by a given cortical focus. Conversely, when the location of the receptive field was more distant, the percentage of responses and the incidence of excitatory effects decreased, inhibitions occurring more frequently. From a functional point of view, such an organization of the cortico-gracile control could be effective in modulating transmission of exteroceptive information from the region of the motor target (facilitation) as well as from adjacent ones (suppression). This arrangement could provide an higher resolution of afferent messages, in relation with the cortically induced movements.     

Motor responses produced by microstimulation of the rostral region of the corpus callosum

In six chronic cats microstimulation experiments were carried out in the rostral portion of the corpus callosum (CC) where fibres run which interconnect the motor cortices of the two hemispheres. Serial dorso-ventral penetrations were stereotaxically performed along the rostro-caudal extent of the CC at 0.25-0.5 mm intervals. Stimulation was delivered at 100 micron steps and, when an effect was present, threshold was determined. Motor responses, consisting of very discrete contractions of shoulder, whisker and eyelid muscles, were obtained upon stimulation of about the most rostral 4 mm at intensities lower than 50 microA. At threshold the responses appeared in only one body region and were often unilateral. A slight increase in current gave rise to symmetrical bilateral effects. Motor effects had thresholds higher than 10 microA. Thresholds were the lowest in the middle portion of CC and gradually rose towards it dorsal and ventral ends. Shoulder and eyelid muscles were represented in the rostral and caudal half of effective zone, respectively, whereas the representation of whisker muscles overlapped with the previous two in the rostral third or the middle part of the effective zone.     

Somatotopic representation of climbing fiber projections from limb cutaneous afferents to the paramedian lobule of the cat cerebellum

Climbing fiber projections to the cerebellar paramedian lobule were investigated electrophysiologically by stimulation of bilateral superficial radial nerve (SR) and superficial peroneal nerve (SP) in the cat anesthetized with pentobarbitone. In the medial zone of the paramedian lobule, short latency climbing fiber responses to stimulation of the ipsilateral SR were recorded rostrally from the top caudal part of the intermediate folia and short latency responses to stimulation of the ipsilateral SP were obtained caudally from the bottom caudal part of the folia. In the central zone, long latency responses to stimulation of the bilateral SR and SP were obtained. "Four limbs area" in which these responses were recorded was 1.0-1.2 mm in width. Short latency responses to stimulation of the ipsilateral SR were observed rostrally from this area, and short and long latency responses to stimulation of the ipsilateral SP were distributed caudally from this area. In the lateral zone, short and long latency responses to stimulation of the ipsilateral SR were recorded rostrally from the rostral part of the intermediate folia, and long latency responses to stimulation of the ipsilateral SP were observed caudally from the caudal part of the folia. In the most lateral zone, short and long latency responses to stimulation of the ipsilateral SR were obtained rostrally from the rostral part of the intermediate folia, and long latency responses to stimulation of ipsilateral SP were recorded only in the bottom caudal part of the folia caudally from the caudal part of the folia.     

Mapping the effects of SI cortex stimulation on somatosensory relay neurons in the rat thalamus: direct responses and afferent modulation

We have used single-unit recording techniques to map the spatial distribution of the primary somatosensory (SI) cortical influences on thalamic somatosensory relay nuclei in the rat. A total of 193 microelectrode penetrations were made to record single neurons in tracks through the medial and lateral ventroposterior (VPL and VPM), ventrolateral (VL), posterior (Po), and reticular (nRt) thalamic nuclei. Single units were classified according to their (1) location within the nuclei, (2) receptive fields, and (3) response to standardized microstimulation in deep layers of the SI cortical forepaw areas. The SI stimulation produced short-latency (1- to 7-msec) excitatory responses in different percentages of neurons recorded in the following thalamic nuclei: VPL, 42.0%; Po, 25.0%; nRt, 16.4%; VL, 13.6%; and VPM, 9.9%. Within the VPL, the highest proportion of responsive neurons was found in the anterior region. Although most of the VL region was unresponsive, the caudal subregion bordering the rostral VPL showed some responsiveness (13.6% of neurons). In general, the spatial pattern of corticothalamic influences appeared to reciprocate the known thalamocortical connection patterns, but with a heterogeneity that was unpredicted. The same parameters of SI cortical stimulation were used in studies of corticofugal modulation of afferent transmission through the VPL thalamus. A condition-test (C-T) paradigm was implemented in which the cortical stimulation (C) was delivered at a range of time intervals before test (T) mechanical vibratory stimulation was applied to digit 4 of the contralateral forepaw. The time course of cortical effects was analyzed by measuring the averaged evoked unit responses of thalamic neurons to the T stimuli, and plotting them as a function of C-T intervals from 5 to 50 msec. Of the 20 VPL neurons tested during SI stimulation, the average response to T stimulation was decreased a mean of 36%, with the suppression peaking (at 49% inhibition of the afferent response) about 15 msec after the C stimulus. Considerable rostrocaudal variation was observed, however. Whereas neurons in the rostral VPL (near VL) were strongly inhibited (-69%), neurons in the middle and caudal VPL exhibited facilitations at long and short C-T intervals, respectively. This study establishes a specific projection system from the forepaw region of SI cortex to different subregions of the VPL thalamus, producing specific temporal patterns of sensory modulation.     

Mapping the Effects of SI Cortex Stimulation on Somatosensory Relay Neurons in the Rat Thalamus: Direct Responses and Afferent Modulation

We have used single-unit recording techniques to map the spatial distribution of the primary somatosensory (SI) cortical influences on thalamic somatosensory relay nuclei in the rat. A total of 193 microelectrode penetrations were made to record single neurons in tracks through the medial and lateral ventroposterior (VPL and VPM), ventrolateral (VL), posterior (Po), and reticular (nRt) thalamic nuclei. Single units were classified according to their (1) location within the nuclei, (2) receptive fields, and (3) response to standardized microstimulation in deep layers of the SI cortical forepaw areas. The SI stimulation produced short-latency (1- to 7-msec) excitatory responses in different percentages of neurons recorded in the following thalamic nuclei: VPL, 42.0%; Po, 25.0%; nRt, 16.4%; VL, 13.6%; and VPM, 9.9%. Within the VPL, the highest proportion of responsive neurons was found in the anterior region. Although most of the VL region was unresponsive, the caudal subregion bordering the rostral VPL showed some responsiveness (13.6% of neurons). In general, the spatial pattern of corticothalamic influences appeared to reciprocate the known thalamocortical connection patterns, but with a heterogeneity that was unpredicted.

The same parameters of SI cortical stimulation were used in studies of corticofugal modulation of afferent transmission through the VPL thalamus. A condition—test (C-T) paradigm was implemented in which the cortical stimulation (C) was delivered at a range of time intervals before test (T) mechanical vibratory stimulation was applied to digit 4 of the contralateral forepaw. The time course of cortical effects was analyzed by measuring the averaged evoked unit responses of thalamic neurons to the T stimuli, and plotting them as a function of C-T intervals from 5 to 50 msec. Of the 20 VPL neurons tested during SI stimulation, the average response to T stimulation was decreased a mean of 36%, with the suppression peaking (at 49% inhibition of the afferent response) about 15 msec after the C stimulus. Considerable rostrocaudal variation was observed, however. Whereas neurons in the rostral VPL (near VL) were strongly inhibited (-69%), neurons in the middle and caudal VPL exhibited facilitations at long and short C-T intervals, respectively. This study establishes a specific projection system from the forepaw region of SI cortex to different subregions of the VPL thalamus, producing specific temporal patterns of sensory modulation.     

Afferents from a single muscle of the forelimbs and fastigial neurons of the cerebellum

Responses of neurons in the medial nucleus of cerebellum (CBM) were studied on stimulation of ipsilateral and contralateral homonymous muscles, in decerebrated cats. The aim was to find out to what extent information from homonymous muscles of the forelimbs converge on the same CBM neurons and whether the probability of such a convergence depends on location (axial, proximal, distal) or function (flexor, extensor) of the tested muscles. The analysis was limited to the neurons belonging to the rostral part of the nucleus which is known to control the ipsilateral muscle periphery. Neuronal activity was recorded extracellularly using tungsten microelectrodes (5-12 M omega) and muscle stimulation was performed by bipolar coated steel electrodes, with the exception of the tip. At least 6 pairs of homonymous muscles were generally stimulated: two axial, two proximal and two distal in both forelimbs. Care was taken that, when a muscle was stimulated, the others were not activated either directly or in a reflex way. Out of the 65 neurons studied, 60 (92%) were responsive to muscle stimulation. It was specifically observed that a high percentage of cells reacted to stimulation of distal muscles (74% to ipsilateral and 71% to contralateral ones). More than half (55%) of the neurons were responsive to activation of a pair of homonymous distal muscles and about one third of them (31%) to both the pairs of distal muscles. On the contrary the percentage of responses to proximal muscles was reduced foremost in the ipsilateral ones (23%) and only an exiquous percentage of cells (15%) received information from the homonymous proximal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

The projection of spinocerebellar neurons from the sacrococcygeal region of the spinal cord in the cat. An experimental study using anterograde transport of WGA-HRP and degeneration.

The projection from the sacro-coccygeal region of the spinal cord to the cerebellum was studied by two different techniques in the cat. In five cats wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) was injected caudal to a preceding unilateral cordotomy at the sacral level, aimed at interrupting the spinocerebellar tracts on one side completely, and the distribution of WGA-HRP labeled mossy fibers and mossy fiber terminals was studied in the cerebellum. In three additional cats, degenerating fibers were examined in Fink-Heimer stained sections following unilateral transection of the lateral and ventral funiculi at L7 or S3 level. In the WGA-HRP experiments the labeled mossy fiber terminals were located bilaterally in lobules I-V. Most of them were found in the anterior part of lobule II. In addition, labeled terminals were observed in sublobule VIIIB and in pars copularis of the paramedian lobule, contralateral to the cordotomy. The terminals in the anterior lobe were concentrated in longitudinal zones parallel to the mid sagittal plane. In lobule II, the terminals were most abundant in the superficial, apical parts of the folia. Some presumed terminals were also seen in the cerebellar nuclei. Labeled fibers were found contralateral, but not ipsilateral to the cordotomy in the superior and inferior cerebellar peduncles, as well as in the spinal cord rostral to the cordotomy. The results of the degeneration experiments were the same as those of the WGA-HRP experiments with regard to the detailed projections in the cerebellar cortex. This is strong support against the possibility that WGA-HRP labeled cerebellar mossy fiber terminals, following WGA-HRP injections in the spinal cord, would represent terminals of collaterals of retrogradely labeled neurons. It also lends strong support in favour of WGA-HRP as a reliable anterograde tracer for studying cerebellar cortical projections of spinocerebellar neurons in the cat.     

Rhythmic arm swing enhances long latency facilitatory effect of transcranial magnetic stimulation on soleus motoneuron pool excitability

The purpose of this study was to investigate whether rhythmic arm swing modulates the long latency effect of transcranial magnetic stimulation (TMS) on soleus motoneuron pool excitability. Ten healthy humans rhythmically swung the left arm back and forth in a sitting position. The soleus H-reflex was evoked when the arm was in the backward swing phase. Conditioning TMS was delivered over the motor cortex 8?ms before the soleus H-reflex was evoked. The soleus H-reflex amplitude in both legs was depressed by the rhythmic arm swing. In contrast, rhythmic arm swing enhanced the facilitatory effect of conditioning TMS over the motor cortex contralateral to the arm swing side on the soleus H-reflex ipsilateral to the arm swing side. This finding indicates that rhythmic arm swing enhances some polysynaptic facilitatory pathways from the motor cortex contralateral to the arm swing side to the soleus motoneuron pool ipsilateral to the arm swing side.     

Rhythmic arm swing enhances long latency facilitatory effect of transcranial magnetic stimulation on soleus motoneuron pool excitability

The purpose of this study was to investigate whether rhythmic arm swing modulates the long latency effect of transcranial magnetic stimulation (TMS) on soleus motoneuron pool excitability. Ten healthy humans rhythmically swung the left arm back and forth in a sitting position. The soleus H-reflex was evoked when the arm was in the backward swing phase. Conditioning TMS was delivered over the motor cortex 8 ms before the soleus H-reflex was evoked. The soleus H-reflex amplitude in both legs was depressed by the rhythmic arm swing. In contrast, rhythmic arm swing enhanced the facilitatory effect of conditioning TMS over the motor cortex contralateral to the arm swing side on the soleus H-reflex ipsilateral to the arm swing side. This finding indicates that rhythmic arm swing enhances some polysynaptic facilitatory pathways from the motor cortex contralateral to the arm swing side to the soleus motoneuron pool ipsilateral to the arm swing side.     

Repetitive microstimulation alters the cortical representation of movements in adult rats

In order to examine the effects of repetitive stimulation on functional cortical organization, standard intracortical microstimulation (ICMS) techniques were used to generate maps of movement representations in motor cortex of rat. After identification of caudal and rostral forelimb fields and adjacent vibrissae and neck fields, one or more representational borders were defined in greater detail. Then a microelectrode was introduced into one of these representational fields, and ICMS current pulses were delivered at a rate of 1/sec for 1 to 3 hr. Following repetitive ICMS, significant changes in movement representations were observed using current levels that were either suprathreshold or subthreshold for evoking the site-specific movement. Electromyographic activity could be evoked at suprathreshold and near-threshold current levels, but not at the subthreshold current levels used here. Significant border shifts ranged from 210 to 670 microns. In each case in which shifts occurred, there appeared to be expansion of the movement represented at the repetitively stimulated site. The effects were progressive and reversible. These results suggest that at least under these unusual experimental circumstances, large representational changes can be generated very rapidly within motor cortex in the absence of any evident peripheral feedback.     

Repetitive Microstimulation Alters the Cortical Representation of Movements in Adult Rats

In order to examine the effects of repetitive stimulation on functional cortical organization, standard intracortical microstimulation (ICMS) techniques were used to generate maps of movement representations in motor cortex of rat. After identification of caudal and rostral forelimb fields and adjacent vibrissae and neck fields, one or more representational borders were defined in greater detail. Then a microelectrode was introduced into one of these representational fields, and ICMS current pulses were delivered at a rate of 1/sec for 1 to 3 hr. Following repetitive ICMS, significant changes in movement representations were observed using current levels that were either suprathreshold or subthreshold for evoking the site-specific movement. Electromyographic activity could be evoked at suprathreshold and near-threshold current levels, but not at the subthreshold current levels used here. Significant border shifts ranged from 210 to 670 μm. In each case in which shifts occurred, there appeared to be expansion of the movement represented at the repetitively stimulated site. The effects were progressive and reversible. These results suggest that at least under these unusual experimental circumstances, large representational changes can be generated very rapidly within motor cortex in the absence of any evident peripheral feedback.     

Hyperventilation evoked by activation of the vicinity of the caudal inferior olivary nucleus depends on the fastigial nucleus in anesthetized rats.

Several studies have demonstrated that cerebellar deep nuclei, particularly the rostral fastigial nucleus (FNr), are involved in respiratory modulation. These nuclei receive inputs from the contralateral caudal inferior olivary nuclei of the medulla. The objectives of this study were to determine whether electrical and chemical activation of the vicinity of the caudal inferior olivary nuclei (vIOc) affected respiration and, if true, whether the FNr was involved in the vIOc stimulation-evoked ventilatory responses. Experiments were conducted in 30 anesthetized and spontaneously breathing rats. Our results showed that 1) electrical (25 or 100 microA at 10 or 20 Hz for 10 s) and chemical (1 or 100 mM, 25-50 nl N-methyl-D-aspartate) stimulation of the vIOc augmented ventilation predominantly via increasing tidal volume; 2) the responses to the electrical stimulation were almost eliminated by lesion of the contralateral FNr via microinjection of ibotenic acid; and 3) the respiratory responses to electrical stimulation in the vicinity of the rostral IO were 65-70% smaller compared with that evoked by vIOc stimulation. These findings strongly suggest that vIOc neurons play a significant role in modulation of respiratory activity, largely depending on their projections to the FNr.     

Aberrant Crossed Corticospinal Facilitation in Muscles Distant from a Spinal Cord Injury

Crossed facilitatory interactions in the corticospinal pathway are impaired in humans with chronic incomplete spinal cord injury (SCI). The extent to which crossed facilitation is affected in muscles above and below the injury remains unknown. To address this question we tested 51 patients with neurological injuries between C2-T12 and 17 age-matched healthy controls. Using transcranial magnetic stimulation we elicited motor evoked potentials (MEPs) in the resting first dorsal interosseous, biceps brachii, and tibialis anterior muscles when the contralateral side remained at rest or performed 70% of maximal voluntary contraction (MVC) into index finger abduction, elbow flexion, and ankle dorsiflexion, respectively. By testing MEPs in muscles with motoneurons located at different spinal cord segments we were able to relate the neurological level of injury to be above, at, or below the location of the motoneurons of the muscle tested. We demonstrate that in patients the size of MEPs was increased to a similar extent as in controls in muscles above the injury during 70% of MVC compared to rest. MEPs remained unchanged in muscles at and within 5 segments below the injury during 70% of MVC compared to rest. However, in muscles beyond 5 segments below the injury the size of MEPs increased similar to controls and was aberrantly high, 2-fold above controls, in muscles distant (>15 segments) from the injury. These aberrantly large MEPs were accompanied by larger F-wave amplitudes compared to controls. Thus, our findings support the view that corticospinal degeneration does not spread rostral to the lesion, and highlights the potential of caudal regions distant from an injury to facilitate residual corticospinal output after SCI.     

Fas and FasL Expression in the Spinal Cord Following Cord Hemisection in the Monkey

The changes of endogenous Fas/FasL in injured spinal cord, mostly in primates, are not well known. In this study, we investigated the temporal changes in the expression of Fas and FasL and explored their possible roles in the ventral horn of the spinal cord and associated precentral gyrus following T(11) spinal cord hemisection in the adult rhesus monkey. A significant functional improvement was seen with the time going on in monkeys subjected to cord hemisection. Apoptotic cells were also seen in the ventral horn of injured spinal cord with TUNEL staining, and a marked increase presents at 7 days post operation (dpo). Simultaneously, the number of Fas and FasL immunoreactive neurons in the spinal cords caudal and rostral to injury site and their intracellular optical density (OD) in the ipsilateral side of injury site at 7 dpo increased significantly more than that of control group and contralateral sides. This was followed by a decrease and returned to normal level at 60 dpo. No positive neurons were observed in precentral gyrus. The present results may provide some insights to understand the role of Fas/FasL in the spinal cord but not motor cortex with neuronal apoptosis and neuroplasticity in monkeys subjected to hemisection spinal cord injury.     

The neurons of origin of non-cortical afferent connections to the oculomotor nucleus. A retrograde labeling study in the rabbit.

The cellular origin of the brainstem projections to the oculomotor nucleus in the rabbit has been investigated by using free (HRP) and lectin-conjugated horseradish peroxidase (WGA-HRP). Following injections of these tracers into the somatic oculomotor nucleus (OMC), retrogradely labeled cells have been observed in numerous brainstem structures. In particular, bilateral labeling has been found in the four main subdivisions of the vestibular complex, predominantly in the superior and medial vestibular nuclei and the interstitial nucleus of Cajal, while ipsilateral labeling was found in the rostral interstitial nucleus of the medial longitudinal fascicle (Ri-MLF), the Darkschewitsch and the praepositus nuclei. Neurons labeled only contralaterally have been identified in the following structures: mesencephalic reticular formation dorsolateral to the red nucleus, abducens internuclear neurons, group Y, several areas of the lateral and medial regions of the pontine and medullary reticular formation, ventral region of the lateral cerebellar nucleus and caudal anterior interpositus nucleus. This study provides also information regarding differential projections of some centers to rostral and caudal portions of the OMC. Thus, the rostral one-third appears to receive predominant afferents from the superior and medial vestibular nuclei, while the caudal two-thirds receive afferents from all the four vestibular nuclei. Finally, the group Y sends afferents to the middle and caudal, but not to the rostral OMC.     

Organization of the sensory and motor nuclei of the glossopharyngeal and vagal nerves in lampreys

Anterograde and retrograde transport of horseradish peroxidase was used to examine the afferent and efferent projections of the glossopharyngeal and vagal nerves in the lamprey, Lampetra japonica. Except for the ganglion cells and motoneurons, the distribution patterns of HRP-positive elements differed little between the two nerves. Afferent fibers mainly terminated in the ipsilateral cerebellar area, medial octavolateralis nucleus, and between the ventral octavolateralis nucleus and descending tract and nucleus of the trigeminal nerve (dV). In the cerebellar area, most of the labeled fibers were located in the molecular zone, but some penetrated into the granular zone. In the rostral part of the medial octavolateralis nucleus, labeled fibers coursed from the middle to the lateral area, and in the caudal part, they were localized in the dorsal area of the nucleus. In the area between the dV and ventral octavolateralis nucleus, labeled fibers coursed near the dorsal margin of the rostral part of the dV, and in the caudal part, they shifted dorsally. Ganglion cells and motoneurons of each nerve were also labeled.     

The organization and connections of somatosensory cortex in the brush-tailed possum (Trichosurus vulpecula): evidence for multiple, topographically organized and interconnected representations in an Australian marsupial

Microelectrode mapping techniques were used to determine the organization of somatosensory cortex in the Australian brush-tailed possum (Trichosurus vulpecula). The results of electrophysiological mapping were combined with data on the cyto- and myeloarchitecture, and patterns of corticocortical connections, using sections cut tangential to the pial surface. We found evidence for three topographically organized representations of the body surface that were coextensive with architectonic subdivisions. A large, discontinuous cutaneous representation in anterior parietal cortex was termed the primary somatosensory area (SI). Lateral to SI we found evidence for two further areas, the second somatosensory area (SII) and the parietal ventral area (PV). While neurones in all of these areas were responsive to cutaneous stimulation, those of SI were non-habituating, whereas those in SII and PV often habituated to the stimuli. Moreover, neuronal receptive fields in SII and PV were, in general, larger than those in SI. Neurones in cortex adjacent to the rostral and caudal boundaries of SI, including cortex that interdigitated between the discontinuous SI head and body representations, required stimulation of deep receptors in the periphery to elicit responses. Within the region of cortex containing neurones responsive to stimulation of deep receptors, body parts were represented in a mediolateral progression. Injections of anatomical tracers placed in electrophysiologically identified locations in SI revealed ipsilateral connections with other parts of SI, as well as cortex rostral to, caudal to, and interdigitating between, SI. Injections in SI also resulted in labelling in PV, SII, motor cortex, posterior parietal cortex and perirhinal cortex. The patterns of contralateral projections reflected those of ipsilateral projections, although they were relatively less dense. The present findings support recent observations in other marsupials in which multiple representations of the body surface were described, and suggest that multiple interconnected sensory representations may be a common feature of cortical organization and function in marsupials.